Exchange surfaces and breathing

Question 1

Why do multicellular organisms need specialised exchange surfaces

Answer 1

Organisms need to take up and get rid of certain substances. Single celled organisms have a large SA:Vol ratio, and can exchange these substances over their outer surface. However, as an organism gets bigger, their SA:Vol ratio gets smaller, and the organisms therefore can’t exchange all the substances it needs to over its outer surface fast enough. Also, substances have further to travel in large organisms (from the edge to the centre).

Question 2

Features of a good exchange surface

Answer 2

• Large SA for molecules to pass through (e.g. folded walls)
• Thin barrier (reduced diffusion distance)
• Fresh supply of molecules on one side (concentration is high) and removal of molecules on the other side (concentration is low) so concentration gradient is maintained.
• Some use active transport to increase exchange

Question 3

Exchange surface

Answer 3

A specialised area that is adapted to make it easier for molecules to cross from one side of the surface to the other

Question 4

Lungs: large SA

Answer 4

Alveoli are very small - 100-300um, and there are many of them. Total SA is much larger than that of the skin (approx 70 metres squared)

Question 5

Lungs: thin barrier

Answer 5

• alveolus wall 1 cell thick
• capillary wall 1 cell thick
• squamous epithelial cells (flat and thin)
• capillaries in close contact to alveoli
• capillaries very narrow so red blood cells press against edges (closer and move slower)
• total diffusion distance is less than 1um thick

Question 6

Lungs: maintaining diffusion gradient

Answer 6

-blood bringing constant supply of CO2, so higher concentration than the air in alveoli
-blood taking away O2, so concentration of O2 is lower in blood than in air in alveoli
-ventilation of the lungs by breathing gives constant supply of O2, so concentration is higher in alveoli than in blood, and removes CO2, so concentration is lower in alveoli than in blood
All these help maintain a high diffusion gradient

Question 7

Structure of trachea and bronchi

Answer 7

• Cartilage in wall, in incomplete rings (less regular in bronchi)
• Glandular tissue, connective tissue, elastic fibres, smooth muscle and blood vessels on the inside of cartilage - loose tissue
• Inner lining of epithelium: ciliated epithelium and goblet cells

Question 8

Structure of bronchioles

Answer 8

• Narrower than bronchi
• no cartilage in small bronchioles
• walls of smooth muscle and elastic fibres
• smallest bronchioles have alveoli at the ends.

Question 9

Structure of alveoli

Answer 9

• coated with surfactant to stop lungs from collapsing
• grape like structure to increase SA
• squamous epithelium on walls to reduce diffusion distance
• moist, so oxygen dissolves and diffuses faster
• good blood supply so continuous removal of O2, increasing diffusion gradient

Question 10

Function of cartilage

Answer 10

Holds trachea and bronchi open, so they don’t collapse on inhalation (low pressure)
Not in a complete ring, so can still move your neck and oesophagus can expand during swallowing

Question 11

Function of smooth muscle

Answer 11

Contracts, constricting airways, making lumen narrower. Restrict air flow to and from alveoli. Prevents harmful substances in air damaging alveoli

Question 12

Function of elastic fibres

Answer 12

Recoil, expelling air

Question 13

Function of goblet cells and glandular tissue

Answer 13

Secrete mucus, trapping tiny air particles and bacteria so lungs aren’t infected/damaged

Question 14

Function of ciliated epithelium

Answer 14

Consists of ciliated cells. Have hair-like structures from membrane called cilia. Move together, wafting mucus up the trachea to be swallowed (stomach acid kills bacteria).

Question 15

Mechanism of inspiration

Answer 15

• diaphragm contracts, flattens, pushing digestive organs down
• external intercostal muscles contract, raising rib cage
• volume of thorax (chest cavity) increases
• pressure in thorax drops below atmospheric pressure
• air moves into lungs

Question 16

Mechanism of expiration

Answer 16

• diaphragm relaxes and is pushed up by displaced organs
• external intercostal muscles relax; ribs fall (on forced expiration, internal intercostal muscles contract)
• volume of chest cavity decreases
• pressure in lungs increases above atmospheric pressure
• air moves out of lungs

Question 17

Tidal volume

Answer 17

Volume of air moved in and out of lungs with each breath when you are at rest (approx 0.5dm3). Provides body with enough O2 for resting needs, and removes CO2 so levels are safe

Question 18

Vital capacity

Answer 18

Largest volume of air that can be moved into and out of the lungs in any one breath (approx 5dm3). Increases with regular exercise, and varies from men to women and with size and age

Question 19

Measuring vital capacity

Answer 19

With a spirometer. Chamber floating on water moves up and down with breathing, get person to take a really big breath, measure vital capacity from graph

Question 20

Measuring tidal volume

Answer 20

With a spirometer. Chamber floating on water moves up and down with breathing, get person to breathe normally, measure tidal volume from graph

Question 21

Measuring oxygen uptake

Answer 21

Carbon dioxide removed from a spirometer with soda lime (otherwise dangerous). O2 in = CO2 out, so can measure the reduction in air in spirometer chamber (CO2 out) and equate it to oxygen used. Can then calculate oxygen uptake by dividing oxygen used by time used up in.

Question 22

Measuring breathing rate

Answer 22

breaths divided by time

Question 23

Setting up a spirometer

Answer 23

• floating chamber, filled with fresh air/medical grade oxygen
• soda lime to remove CO2
• disposable mouthpiece
• nose clip so no breath through nose